a. Field of the Invention
The present disclosure relates generally to medical systems for monitoring and protecting non-targeted tissue during the performance of medical procedures or therapeutic functions, such as, for example, ablation procedures. More particularly, the present disclosure relates to an esophageal monitoring, managing and protecting system for protecting non-targeted esophageal tissue during proximate ablation procedures, such as ablation procedures in the atrium.
b. Background Art
It is known to use minimally invasive surgical devices or ablating tools to perform ablation procedures in, for example, the heart. For instance, in treating a condition known as atrial fibrillation, it is known to advance an ablating tool through the vasculature of a patient to a desired location, and to then thermally ablate tissue within, for example, an ostium connecting a pulmonary vein to the heart, or to ablate the tissue within the heart surrounding the ostium.
Examples of the types of tools known in the art to perform such procedures are catheter-based ablating devices such as those described in U.S. Pat. No. 6,635,054 entitled “Thermal Treatment Methods and Apparatus with Focused Energy Application,” U.S. Patent Publication No. 2004/0176757 entitled “Cardiac Ablation Devices,” and International Publication No. WO 2005/102199 entitled “Ablation Devices with Sensor Structures.” These devices generally include, among other components, an elongate shaft having a proximal end, a distal end, and a longitudinal axis extending therebetween. The devices further include an ablation element mounted at or near the distal end of the elongate shaft. In at least one such device, the ablation device is configured to emit ultrasonic waves with the strength and intensity to burn or ablate targeted tissue. Other ablation devices perform similar functions through the emission of RF energy.
In operation, once an ablating device is positioned in a desired location within the patient's anatomy (e.g., in the atrium), the ablation device is selectively activated to emit ablating energy (e.g., intense ultrasonic or RF energy). The energy is then directed forward and focused to define, for example, a region in the circumferential interior OS annular wall. Such a circumferential ablating device provides an efficient and effective means by which to simultaneously circumferentially ablate myocardial tissue around the OS of the pulmonary vein. Typically, multiple pulmonary ostia are ablated separately and sequentially with the same device as it is moved and placed in each OS needing ablation.
However, these known devices are not without their drawbacks. For instance, a drawback in known endocardial catheter pulmonary vein ostia ablation systems relates to the monitoring, maintenance, and/or control of the temperature in non-targeted tissue proximate the targeted ablation site during the ablation procedure. Such non-targeted tissue must not be damaged during the ablation procedure. More particularly, when certain heart tissue is being ablated, the energy emitted from the ablating device may be strong enough or generate a high enough temperature to cause tissue necrosis in non-targeted tissue.
As an example, since the esophagus which is generally located posterior to the atrium, RF ablation on the posterior atrial wall has been known to cause serious complications such as esophageal fistula. Such complications have even led to death of patients following RF ablation for treatment of Atrial Fibrillation (AF). Such complications are created by thermally-mediated damage to the esophagus due to overheating of the esophagus from uncontrollable application of RF energy during ablation on the posterior atrial wall.
Thermal monitoring of the esophagus to monitor and prevent such overheating has been proposed and tried, for example, the ProRhythm Esophageal Balloon. Such thermal monitoring techniques provide means of monitoring the temperature of the esophageal luminal wall. However, thermal monitoring of the luminal wall of the esophagus is generally inadequate in preventing such esophageal complications caused by ablation of the atrial wall.
At the outset, the temperature measurement of the esophageal wall is generally unreliable due the difficulty in accurately positioning the thermal probe in the esophagus relative to the ablation site on the atrial wall.
Even if the thermal probes are properly positioned in the esophagus, the threshold cut-off temperature to prevent esophageal complications cannot be set a priori. This is due to several factors, including that the thickness of the different tissue layers, such as for example, the pericardium, the fat layer, and the connective tissue, between the ablation electrode on the endocardial surface and the thermal sensors on the luminal wall of the esophagus, is not readily known. Further, the electric field and thermal properties of these tissue layers are not readily known. Based on these unknown variables, the thermal gradient from the endocardial site to the esophageal wall often cannot be readily determined. Consequently, the maximum temperature that can be allowed on the endocardial wall without creating dangerously high temperatures on the esophagus cannot be readily determined. The difficulty of reliably determining such temperatures on the endocardial side is further compounded by the unreliability of determining the endocardial tissue temperature during ablation.
If the thermal probes could reliably measure temperature of the esophageal luminal wall, that thermal information arrives after the fact that the esophageal wall has already attained potentially harmful temperature. This is due to the diffusive nature of the thermal field which has a long time constant. Thus, by the time the thermal probe senses a temperature rise in the luminal wall of the esophagus, it is usually too late for any preventative or corrective action.
Because of the aforementioned limitations, thermal monitoring of the esophageal luminal wall fails to provide a priori information that can be reliably used to adequately protect and prevent thermally-mediated esophageal injury during endocardial RF ablation of the posterior atrial wall during atrial fibrillation treatment. Accordingly, there is a need for an ablation tool, component and/or a system that will monitor, manage and/or protect non-targeted tissue during a medical procedure that functions to minimize or eliminate one or more of the above-identified deficiencies.
The present disclosure overcomes the above-described and other limitations of current monitoring and protecting of non-targeted tissue, such as the esophageal luminal wall, by electrically monitoring the targeted and/or non-targeted tissue conditions between the ablation electrode and the monitoring electrode, such as the tissue of and between the endocardial wall and the luminal wall of the esophagus, before and during ablation, and taking protective measures when necessary.